The long-term goal of the proposed research is to gain understanding of the process of regeneration of sensory and nerve cells following mechanical injury to the cochlea in culture, and to define the factors that lead to their morphological recovery. In light of the lack of overt evidence proving that the mammalian organ of Corti is able to form new sensory cells, and given the fact that these cells are few and may be formed only once in a life span the significance of the research lies in understanding the mechanism of survival and recovery of receptor cells after injury. Specifically, we propose to study: 1) Post-traumatic cell proliferation in the organ of Corti: A) Mitotic cell proliferation in the injured cultures will be examined using 3H thymidine to investigate the identity of dividing cells, the duration of the mitotic response and the age- related occurrence of cell division; B) Nonmitotic cell proliferation, expressed by extensive sprouting of supporting cells, will be investigated in search of possible diffusable growth factors (NGF, EGF, FGF) released by the cells in response to direct injury or to the injury of sensory cells. 2) Regeneration of the injured sensory cells, especially the reformation of their cuticular plates and stereocilia. The study will encompass the morphological sequence of the regenerative phenomena, its comparison with normal development, and the influence of age on the regenerative capacity of sensory cells. 3) Degeneration and regeneration of spiral neurons, sprouting of their endings (using antibodies to GAP-43 and NF proteins), and formation of new ribbon synapses. The study will be done using short- and long-term cultures of the mouse organ of Corti. The injury will be done by hand, using either a pulled- glass pipettes or a laser. Light and electron microscopy, autoradiography, biochemistry and immunocytochemistry will be employed. Some specialized immunological assays will be done in collaboration with Dr. Philippe Lefebvre, University de Liege, Belgium.